The present invention is in the field of image intensifier tubes, and particularly is directed to an improved contact assembly for an image intensifier tube, and to a method of making such assembly.
Image intensifier tubes are utilized to enhance night time vision without using additional light. These devices have both military and industrial applications. The U.S. military uses image intensifier tubes for viewing and aiming at targets at night that otherwise would not be visible. In addition, image intensifier tubes are used by aviators to enhance night time vision, for providing night vision to people who suffer from night blindness (retinitis pigmentosa) and for photographing astronomical bodies.
Generally, an image intensifier tube includes three main components. These components include a photocathode, a phosphor screen (anode) and a microchannel plate (MCP) disposed between the photocathode and anode. The photocathode is a photoemissive waver that is extremely sensitive to low radiation levels of light in the 580-590 nm spectral ranges. When electromagnetic radiation impinges on the photocathode, the photocathode emits electrons in response.
The MCP is a relatively thin glass plate having input and output planes and an array of microscopic holes through it. An electron impinging on the MCP results in the emission of a number of secondary electrons which, in turn, cause the emission of more secondary electrons. Therefore, each microscopic hole acts as a channel type secondary emission electron multiplier having an electron gain of approximately several hundred. The electron gain is primarily controlled by a potential difference between the input and output planes of the MCP. Consequently, the MCP increases the density of electron emission.
The anode includes an output fiber optic window and a phosphor screen which is formed on a surface of the window. Emitted electrons are accelerated towards the phosphor screen by maintaining the phosphor screen at a higher positive potential than the MCP. The phosphor screen converts the electron emission into an image which is visible to an operator.
For the proper operation of the tube, there must be a potential difference across the MCP, and between the MCP and the screen. These voltages are provided by an external power source, typically a low voltage battery located outside the image intensifier tube and a power supply which is located around the periphery of the tube. The power supply includes an electronic chopper, step up transformer, a rectifier, and a voltage regulator to provide the appropriate voltages.
The image intensifier tube is bounded at one end by a back plate which bears a pair of contact assemblies. Power from the external source is provided to the tube by electrically connecting leads from the source to the contact assemblies. The U.S. Military specifies a particular night vision device as AN/PVS-7A. This device utilizes a contact assembly in the form of a pin socket, and power from the external source is applied via a pin which is inserted in the pin socket. Another U.S. Military specified night vision device is AN/PVS-7B, which uses a contact assembly in the form of a flat. Power is applied from the external source via a spring loaded pin contact which pushes against the flat.
To accommodate both the AN/PVS-7A and AN/PVS-7B specifications, a contact assembly known as a universal assembly has been utilized which has both a pin socket, and a flat at one end of the pin socket extending perpendicular thereto. When the universal assembly is seated in the back plate of an image intensifier tube, contact to the assembly may be made either by a pin inserted in the pin socket or by a spring loaded pin contact pushing against the flat.
The universal contact assembly of the prior art is comprised of two pieces which are soldered together. The first piece is a cylindrical pin socket and the second piece is a flat or xe2x80x9cU-tubexe2x80x9d, which is a flat, elongated piece of metal shaped like an elongated letter xe2x80x9cUxe2x80x9d. The flat has a hole in it, and the pin socket is inserted in the hole, whereupon the two parts are soldered together. The problem with the prior art structure is that the solder joint is not clean and therefore when the contact assembly is mounted in the back plate of the image intensifier tube, it does not seat squarely, and may move or become loose, adversely affecting tube operation.
Also, in the universal contact assembly of the prior art, the flat is at one end of the pin socket, while at the other end, the exterior surface of the cylindrical pin socket is soldered to a wire leading to the internally located power supply of the image intensifier tube. The wire is held to the pin socket only by solder. Soldering a wire end to a cylindrical rod (the pin socket) is inconvenient to accomplish and may result in breakage of the wires and consequent electrical disconnection during use.
In accordance with the first aspect of the present invention, a universal contact assembly for an image intensifier tube is provided wherein the pin socket and flat are both parts of an integrally formed unit. Hence, the junction of the two parts is clean and solder-free, and the contact assembly seats squarely in the back plate, and does not loosen.
In accordance with a second aspect of the invention, the pin socket is provided with a through hole in which a wire lead fed to the power supply may be inserted before soldering. This enables a quicker and more convenient solder operation, since the lead is held in the hole, with less possibility that the connection will be broken over the life of the tube.
In accordance with a third aspect of the invention, an improved method of making a universal contact assembly is provided.